1. Field of the Invention
This invention relates to an integration circuit for an electric shutter means provided in a photographic camera, and more particularly to a positive feedback circuit for an integration circuit in an electric shutter means built in a photographic camera.
2. Description of the Prior Art
In the conventional electric shutter means for cameras, it has been known to use mechanical switches to make a single operational amplifier have additional functions beside the function of integration. Mechanical switches are, however, disadvantageous in that they cause malfunction of the circuit owing to their chattering and slow response. Therefore, recently semiconductor switches have been substituted for the mechanical switches. The semiconductor switches, however, are not desirable as the switches for an integration circuit operated by small current as employed in an electric shutter means of a photographic camera, since the OFF-resistance of the semiconductor switches is comparatively small. Because of the low OFF-resistance of the semiconductor switches, an integrating capacitor is likely to be undesirably charged by leakage current of the semiconductor switching circuit when the switching circuit is in its OFF state.